My Apple Watch thinks I fell when I clap my hands

Does the watch band sit tight on your wrist?

Did you try to force restart by pressing and holding the Digital Crown and the Side button together for about 10sec, until the Apple logo comes back again?

Did you consider to set the Fall Detection to "Only on during Workouts"?

Use Fall Detection with Apple Watch - Apple Support

High acceleration, then a sudden stop, is indicative of a fall. Depending on how enthusiastic your clapping is, the Apple Watch may think you have fallen.